The Sesquiterpene Synthase PtTPS5 Produces (1 S ,5 S ,7 R ,10 R )-Guaia-4(15)-en-11-ol and (1 S ,7 R ,10 R )-Guaia-4-en-11-ol in Oomycete-Infected Poplar Roots

Pathogen infection often leads to the enhanced formation of specialized plant metabolites that act as defensive barriers against microbial attackers. In this study, we investigated the formation of potential defense compounds in roots of the Western balsam poplar ( ) upon infection with the generalist root pathogen (Oomycetes). infection led to an induced accumulation of terpenes, aromatic compounds, and fatty acids in poplar roots. Transcriptome analysis of uninfected and -infected roots revealed a terpene synthase gene that was significantly induced upon pathogen infection. PtTPS5 had been previously reported as a sesquiterpene synthase producing two unidentified sesquiterpene alcohols as major products and hedycaryol as a minor product. Using heterologous expression in , enzyme assays with deuterium-labeled substrates, and NMR analysis of reaction products, we could identify the major PtTPS5 products as (1 ,5 ,7 ,10 )-guaia-4(15)-en-11-ol and (1 ,7 ,10 )-guaia-4-en-11-ol, with the former being a novel compound. The transcript accumulation of in uninfected and -infected poplar roots matched the accumulation of (1 ,5 ,7 ,10 )-guaia-4(15)-en-11-ol, (1 ,7 ,10 )-guaia-4-en-11-ol, and hedycaryol in this tissue, suggesting that PtTPS5 likely contributes to the pathogen-induced formation of these compounds in planta.